It was not the size of their bill - although they are fast catching up with those presented in similar establishments in Western countries. It was, rather, an extremely loud blast from a bomb that had been set off just outside the entrance. Several doors and windows were smashed in the blast and a nearby casino and art gallery were badly damaged. Miraculously, nobody was injured.
As with many such incidents, a new phenomenon in Riga since the break with Moscow, the culprits were not caught. A spokesman for the police said they had no information on whether or not the cafe had been subject to demands for protection money. He conceded, eventually, however, that the bombing was 'most probably' the work of 'the mob'.
As in the two other Baltic states, most of Eastern Europe and, of course, the former republics of the Soviet Union, 'the mob' has gained a firm foothold in Latvia since the country formally regained its independence in August 1991.
No one is quite sure what 'the mob' is, who is behind it, or where it will strike next. According to some Western observers, there are at least four or five street mafias operating in Riga, one of which, inevitably, is said to emanate from the self-proclaimed Chechen republic, home to some of the roughest gangsters in the whole of what was the Soviet Union.
Their activities range from small-time racketeering to high-level corruption. The extent to which they work in tandem or against each other is also unclear - although it has not been unkown for members of rival gangs to 'straighten things out' between themselves with the aid of bazookas.
'This is, indeed, the wild, wild West,' commented one American who has spent many years in the Soviet Union and its successor states. 'Whatever tensions there may be between ethnic Latvians and Russians here, the only serious violence is committed by those involved in organised crime.'
While obviously alarming, it would be wrong to exaggerate the scale of the mafia problem. Bombings are not isolated events, but nor are they daily occurrences. And despite having a grip on much of the city's commericial life, 'the mob' does not appear to be stifling it. Far from it.
As with Tallinn to the north, Riga gives the impression of being a boom city - already light years away from its dismal Soviet past.
In the picturesque old town, the rich mix of Gothic, Renaissance, Baroque and Art Nouveau buildings are at last being given a lick of paint and have become transformed into banks, cafes, bars and fancy new shops, well-stocked with Western goods.
This may not be reflected so clearly in other parts of the country, but in Riga, known as the 'Paris of the Baltic' before the war, it is difficult not to feel there are plenty of people making plenty of money.
Where it is all coming from remains unclear. Officially, the Latvian economy, still largely state-owned and almost totally dependent on trade with the East, remains something of a disaster area - vast factories producing Soviet-style goods that Russians can no longer afford and that people in the West would not touch with a barge pole.
Unofficially, however, the entrepreneurial spirit appears to be winning through. Although the country has no reserves of its own, it is apparently now one of the world's main exporters of copper - all of which comes semi-legally through Russia to be shipped on elsewhere.
'Somehow, despite all the difficulties of breaking away from Moscow, despite all the problems with the mafias, commercial activity is thriving,' said the American observer. 'Of all the places in the former Soviet Union, this one is looking most clearly as though it has suddenly rejoined Europe.'